To estimate the weights of fictional little people, the only factual starting point is what real little people weigh. In a letter describing hobbits for illustration, Tolkien stated that he imagined hobbits as "stout, and short of leg." Achondroplasia, the most common form of dwarfism, seems to be the closest comparison that we have, proportionally speaking, since it has both features described by Tolkien, although it has other typical features as well. According to height/weight charts for achondroplasia, a little person weighs about 35 lbs at 3 ft, 45 lbs at 3 1/2 ft, and 55 lbs at 4 ft.
More pertinent to the context of your question: It's not mentioned that Sam or Frodo are significantly shorter than Merry or Pippin, who top 4 ft after drinking the Ent-draft, so it's reasonable to assume that they were all over 3 1/2 ft, possibly closer to 4 ft, at the beginning of the story. For the sake of convenience, we could estimate 50 lbs each, and that's without their clothes and gear, which could add an additional 1/3 pretty easily, based on gear for a long camping trip. So the four hobbits and their gear would be about 267 lbs.
A fine-boned male elf probably wouldn't weigh more than a slim human male of the same height. According to the BMI index for men, a 6' human male can weigh as little as 140 lbs while still being healthy and a 6'3" human male, as little as 150 lbs. Glorfindel is not described as carrying any gear, so with his clothing, he might weigh 160 lbs.
Horses can carry about 20% of their body weight without increasing heart rate and muscle soreness. Based on the description of Glorfindel's horse, it's more of a racehorse than a draft horse. Arabians and thoroughbreds weigh about 950 and 1000 lbs, respectively, so Glorfindel's horse could carry 190-200 lbs without additional fatigue.
Based on those estimates, carrying all four hobbits would have caused additional fatigue. Since the horse would be unable to carry all four hobbits, carrying additional riders--for example, swapping out--wouldn't have provided any benefit to the overall speed of the party because at least one hobbit would be walking at all times.